The present invention relates to an active dynamic damper suitable to actively damp a vibration from a vibration generating source such as a vehicle.
A conventionally known active dynamic damper of this kind comprises mainly an electromagnetic vibration means, which is a vibration means, and an electric control unit. In this electromagnetic vibration means, a yoke which accommodates an electromagnet is mounted on a mounting metal member scheduled to be installed on, for example, a vehicle body, which is a vibration generating source, and a mass member is provided on the yoke such that it is supported elastically by means of a rubber elastic body. The electric control unit inputs an electric control signal into the electromagnet so as to generate a driving force corresponding to the magnitude of the electric control signal. This electromagnetic vibration means is intended to drive the electromagnet and thereby vibrate the mass member in order to actively suppress a vibration of the vibration generating source with a vibration force generated on the mass member.
A linear amplifier such as an audio amplifier can be used as a driver for driving this electromagnetic vibration means, but in this case the driver cost is high because the linear amplifier is expensive. For this reason, if the active dynamic damper is used for a low cost application such as a vehicle application, a pulse width modulation driver (hereinafter referred to as PWM driver) which turns ON/OFF a switching transistor using, for example, a pulse-width modulated control pulse signal is used to generate an electric control signal for driving the electromagnetic vibration means. The control pulse signal for use in this case is formed by overlaying a reference pulse signal on a pulse-width modulated carrier signal having a frequency of several kHz (4-20 kHz) by means of a PWM driver. The reference pulse signal is synchronous with an input pulse signal S, which is an output of a rotation pulse sensor or the like correlated to the vibration frequency of the vibration generation source and at the same time shifted by a phase θ, while the magnitude of a control amplitude corresponding to the vibration amplitude of the vibration generation source is correlated to the magnitude of duty ratio. The conventional dynamic damper vibrates the mass member by driving the vibration means based on this control pulse signal so as to suppress the vibration of the vehicle body with a vibration force based on this vibration. Generally, sampling of the input pulse signal S is carried out under 1-2 kHz.
However, the above-mentioned active dynamic damper has a problem that when such a vibration means having a high linearity is driven by the aforementioned control pulse signal, a chattering vibration and an abnormal sound by such as a sharp sound originated from the carrier frequency of the control pulse signal and a rattling sound originated from the sampling frequency of the inputted pulse signal, are likely to be generated. Another vibration means for a mass member, similar to the electromagnetic vibration means, is a pneumatic vibration means.
In the pneumatic vibration means, the mass member is elastically supported with respect to a mounting member attached to the vibration damping object member. A pneumatic chamber sealed tightly for applying a vibration force to the mass member through changes in internal pressure is provided and a driving selection valve which connects the pneumatic chamber selectively to a negative pressure source or atmosphere is provided in an air flow path. The driving selection valve is controlled according to the aforementioned control pulse signal, so as to adjust the vibration force frequency, phase and amplitude of the mass member. The pneumatic chamber of the pneumatic vibration means is connected to the negative pressure source like an engine suction port and to the atmosphere through the air flow path, and change-over between the negative pressure source and the atmosphere is carried out by the selection valve imposed in the air flow path. Consequently a change in pressure is generated in the pneumatic chamber so as to adjust the vibration force for vibrating the mass member. However, this pneumatic vibration means has the same problem as the above-described electromagnetic vibration means.